1. Technical Field of the Invention
The invention relates to stepper motors, including those used in large industrial internal combustion engines, and more particularly to a method and system for economically determining when the stepper motor does not move in response to a command signal.
2. Description of Related Art
Stepper motors are known in the prior art and have many uses, including in large industrial internal combustion engines for performing some control function such as controlling the regulator position. The latter application typically involves an actuator member sometimes called a xe2x80x9chockey puckxe2x80x9d. The xe2x80x9chockey puckxe2x80x9d is axially movable along a threaded shaft that is rotationally driven by the stepper motor.
A stepper motor is a synchronous motor having a magnetized rotor and a plurality of stator windings, typically four, energized in a designated sequence to make the rotor rotate. Normally, the rotor remains synchronized to the windings as they are energized (in synchronism), so that the rotor""s position is known precisely. However, if the torque load on the rotor output shaft becomes too great, or the motor is accelerated too fast, it is possible for the motor to stall. In the stalled condition, the rotor no longer moves synchronously and may become stationary. There is no in-between state. In other words, the motor is either running in synchronism or it is stalled.
A problem with stepper motors is that it is difficult to determine, without physical inspection, whether the rotor actually moved in response to a command signal energizing the windings. One solution known in the prior art is to install an encoder on the motor, for example a linear variable differential transformer (LVDT), or rotary position encoder. This may be objectionable in numerous applications because of cost.
Therefore, there is a need for a simple and inexpensive manner in which to determine whether a stepper motor is stalled.
The present invention provides an economical method and system for detection of stall in a stepper motors.
The invention embodies a stall detection method for a stepper motor having a rotor and a plurality of energizable stator windings. A stalled condition of the motor is ascertained according to current rise time of the windings. The stator windings are arranged in opposed pairs and the stepper motor is determined to be stalled when the current rise time of one winding in an opposed winding pair is different from the other winding in the opposed winding pair within a cycle of the motor. The stepper motor is determined to be running when the current rise time of all of the windings is substantially equal within a cycle of the motor.
The invention further embodies a stall detection system for a stepper motor having a rotor and a plurality of energizable windings. The system includes a device that ascertains a running condition of the motor when the current rise times of all the windings in the motor are substantially equal within a cycle of the motor and a stalled condition of the motor when the current rise times of one winding is relatively short as compared to a winding opposite the one winding within a cycle of the motor.